/* A C-program for MT19937: Integer version (1999/10/28)          */
/*  genrand() generates one pseudorandom unsigned integer (32bit) */
/* which is uniformly distributed among 0 to 2^32-1  for each     */
/* call. sgenrand(seed) sets initial values to the working area   */
/* of 624 words. Before genrand(), sgenrand(seed) must be         */
/* called once. (seed is any 32-bit integer.)                     */
/*   Coded by Takuji Nishimura, considering the suggestions by    */
/* Topher Cooper and Marc Rieffel in July-Aug. 1997.              */

/* This library is free software; you can redistribute it and/or   */
/* modify it under the terms of the GNU Library General Public     */
/* License as published by the Free Software Foundation; either    */
/* version 2 of the License, or (at your option) any later         */
/* version.                                                        */
/* This library is distributed in the hope that it will be useful, */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of  */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.            */
/* See the GNU Library General Public License for more details.    */
/* You should have received a copy of the GNU Library General      */
/* Public License along with this library; if not, write to the    */
/* Free Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA   */
/* 02111-1307  USA                                                 */

/* Copyright (C) 1997, 1999 Makoto Matsumoto and Takuji Nishimura. */
/* Any feedback is very welcome. For any question, comments,       */
/* see http://www.math.keio.ac.jp/matumoto/emt.html or email       */
/* matumoto@math.keio.ac.jp                                        */

/* REFERENCE                                                       */
/* M. Matsumoto and T. Nishimura,                                  */
/* "Mersenne Twister: A 623-Dimensionally Equidistributed Uniform  */
/* Pseudo-Random Number Generator",                                */
/* ACM Transactions on Modeling and Computer Simulation,           */
/* Vol. 8, No. 1, January 1998, pp 3--30.                          */

#include<stdio.h>

/* Period parameters */
#define N 624
#define M 397
#define MATRIX_A 0x9908b0df	/* constant vector a */
#define UPPER_MASK 0x80000000	/* most significant w-r bits */
#define LOWER_MASK 0x7fffffff	/* least significant r bits */

/* Tempering parameters */
#define TEMPERING_MASK_B 0x9d2c5680
#define TEMPERING_MASK_C 0xefc60000
#define TEMPERING_SHIFT_U(y)  (y >> 11)
#define TEMPERING_SHIFT_S(y)  (y << 7)
#define TEMPERING_SHIFT_T(y)  (y << 15)
#define TEMPERING_SHIFT_L(y)  (y >> 18)

static unsigned long mt[N];	/* the array for the state vector  */
static int mti = N + 1;		/* mti==N+1 means mt[N] is not initialized */
	
/* Initializing the array with a seed */
void sgenrand(unsigned long seed)
{
	int i;

	for (i = 0; i < N; i++) {
		mt[i] = seed & 0xffff0000;
		seed = 69069 * seed + 1;
		mt[i] |= (seed & 0xffff0000) >> 16;
		seed = 69069 * seed + 1;
	}
	mti = N;
}

/* Initialization by "sgenrand()" is an example. Theoretically,      */
/* there are 2^19937-1 possible states as an intial state.           */
/* This function allows to choose any of 2^19937-1 ones.             */
/* Essential bits in "seed_array[]" is following 19937 bits:         */
/*  (seed_array[0]&UPPER_MASK), seed_array[1], ..., seed_array[N-1]. */
/* (seed_array[0]&LOWER_MASK) is discarded.                          */
/* Theoretically,                                                    */
/*  (seed_array[0]&UPPER_MASK), seed_array[1], ..., seed_array[N-1]  */
/* can take any values except all zeros.                             */
void lsgenrand(unsigned long seed_array[])
    /* the length of seed_array[] must be at least N */
{
	int i;

	for (i = 0; i < N; i++)
		mt[i] = seed_array[i];
	mti = N;
}

unsigned long genrand(void)
{
	unsigned long y;
	static unsigned long mag01[2] = { 0x0, MATRIX_A };
	/* mag01[x] = x * MATRIX_A  for x=0,1 */

	if (mti >= N) {		/* generate N words at one time */
		int kk;

		if (mti == N + 1)	/* if sgenrand() has not been called, */
			sgenrand(4357);	/* a default initial seed is used   */

		for (kk = 0; kk < N - M; kk++) {
			y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
			mt[kk] = mt[kk + M] ^ (y >> 1) ^ mag01[y & 0x1];
		}
		for (; kk < N - 1; kk++) {
			y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
			mt[kk] = mt[kk + (M - N)] ^ (y >> 1) ^ mag01[y & 0x1];
		}
		y = (mt[N - 1] & UPPER_MASK) | (mt[0] & LOWER_MASK);
		mt[N - 1] = mt[M - 1] ^ (y >> 1) ^ mag01[y & 0x1];

		mti = 0;
	}

	y = mt[mti++];
	y ^= TEMPERING_SHIFT_U(y);
	y ^= TEMPERING_SHIFT_S(y) & TEMPERING_MASK_B;
	y ^= TEMPERING_SHIFT_T(y) & TEMPERING_MASK_C;
	y ^= TEMPERING_SHIFT_L(y);

	return y;
}

	